hash-pred: Generalise and simplify.

utils.rkt

@@ -27,18 +27,15 @@
 ;;; essentially to avoid having to write explicit hash-ref calls.
 
 ;;; Checks whether dict is a hash table and whether its keys satisfy
-;;; key-pred and its values satisfy val-pred.  If one of the
-;;; predicates is #f, it is not checked.  For example, (hash-pred
-;;; dict) is equivalent to (hash dict).
-(define (hash-pred dict #:key-pred [key-pred #f] #:val-pred [val-pred #f])
-  (and (hash? dict)
-       (if (not (hash-empty? dict))
-           (if key-pred
-               (key-pred (car (hash-keys dict)))
-               #t)
-           (if val-pred
-               (val-pred (car (hash-values dict)))
-               #t))))
+;;; key-pred and its values satisfy val-pred.  If either of the
+;;; predicates is not supplied, it defaults to true.  For example,
+;;; (hash-pred dict) is equivalent to (hash dict).
+(define/match (hash-pred dict
+                         #:key-pred [key-pred (λ (_) #t)]
+                         #:val-pred [val-pred (λ (_) #t)])
+  [((hash-table (keys vals) ...) key-pred val-pred)
+   (and (andmap key-pred keys) (andmap val-pred vals))]
+  [(_ _ _) #f])
 
 ;;; A variable mapping is a hash table mapping symbols to values.
 (define (variable-mapping? dict) (hash-pred dict #:key-pred symbol?))